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.Dd September 7, 2021
.Dt MPROTECT 2
.Os
.Sh NAME
.Nm mprotect
.Nd control the protection of pages
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/mman.h
.Ft int
.Fn mprotect "void *addr" "size_t len" "int prot"
.Sh DESCRIPTION
The
.Fn mprotect
system call
changes the specified pages to have protection
.Fa prot .
.Pp
The
.Fa prot
argument shall be
.Dv PROT_NONE
(no permissions at all)
or the bitwise
.Em or
of one or more of the following values:
.Pp
.Bl -tag -width ".Dv PROT_WRITE" -compact
.It Dv PROT_READ
The pages can be read.
.It Dv PROT_WRITE
The pages can be written.
.It Dv PROT_EXEC
The pages can be executed.
.El
.Pp
In addition to these standard protection flags,
the
.Fx
implementation of
.Fn mprotect
provides the ability to set the maximum protection of a region
(which prevents
.Nm
from adding to the permissions later).
This is accomplished by bitwise
.Em or Ns 'ing
one or more
.Dv PROT_
values wrapped in the
.Dv PROT_MAX()
macro into the
.Fa prot
argument.
.Sh RETURN VALUES
.Rv -std mprotect
.Sh ERRORS
The
.Fn mprotect
system call will fail if:
.Bl -tag -width Er
.It Bq Er EACCES
The calling process was not allowed to change
the protection to the value specified by
the
.Fa prot
argument.
.It Bq Er EINVAL
The virtual address range specified by the
.Fa addr
and
.Fa len
arguments is not valid.
.It Bq Er EINVAL
The
.Fa prot
argument contains unhandled bits.
.It Bq Er ENOTSUP
The
.Fa prot
argument contains permissions which are not a subset of the specified
maximum permissions.
.El
.Sh SEE ALSO
.Xr madvise 2 ,
.Xr mincore 2 ,
.Xr msync 2 ,
.Xr munmap 2
.Sh HISTORY
The
.Fn mprotect
system call was first documented in
.Bx 4.2
and first appeared in
.Bx 4.4 .
.Pp
The
.Dv PROT_MAX
functionality was introduced in
.Fx 13 .
